Liquid crystal display cell spacer and liquid crystal display cell

ABSTRACT

The present invention relates to a liquid crystal display cell spacer with improved in coloring effect and light shielding effect and optimal electrical, physical, chemical, and optical properties and a liquid crystal display cell with use thereof. A liquid crystal display cell spacer comprising surface-coated carbon black; a liquid crystal display cell spacer comprising a pigment component comprising carbon black and at least one set of organic pigments of dissimilar colors other than carbon black; and a liquid crystal display cell spacer comprising a pigment component comprising surface-coated carbon black and at least one set of organic pigments of dissimilar colors other than carbon black. A liquid crystal display cell with use any of above liquid crystal display cell spacers.

TECHNICAL FIELD

The present invention relates to a liquid crystal display cell spacerwith improved in coloring effect and light shielding effect and to aliquid crystal display cell with use thereof.

BACKGROUND ART

While the liquid crystal display cell has been used widely in a varietyof electronic equipment such as personal computers and portableelectronic devices, there has been much need for improving itsperformance by increasing its display contrast of images. Japanese KokaiPublication Sho-57-189117 discloses such a technology which comprisesdisposing two transparent electrode-carrying substrates with therespective electrodes facing each other and a liquid crystalhermetically sandwiched between said substrates, with particles of acolored spacer being dispersed on the entire surfaces of the substrateswhich are adjoining to the liquid crystal so as to prevent deteriorationof the display contrast of images.

The liquid crystal display cell spacer for such a high-contrast liquidcrystal display cell must have been colored to a deep shade. While manyproduction methods have heretofore been proposed for the fabrication ofsuch a liquid crystal display cell spacer, they can be roughly dividedinto the technology which comprises dyeing polymer particles previouslymanufactured and the technology which comprises dyeing polymer particlesin the course of their manufacture.

The technology which comprises dyeing polymer particles previouslymanufactured includes the following processes.

Japanese Kokai Publication Hei 1-144429 describes a process whichcomprises treating polymer particles with an acid and then dyeing them.Japanese Kokai Publication Hei-1-207719 discloses a process whichcomprises subjecting polymer particles to heat treatment at 200 to 700°C. to provide flame-resistant sintered particles. Japanese KokaiPublication Hei-5-165033 discloses a process which comprises coatingpolymer particles with a conjugated polymer such as polyacetylene.Japanese Kokai Publication Hei-1-200227 describes a process whichcomprises disposing a metallic layer on the surface of crosslinkedpolymer particles and oxidizing the metal to the metal oxide.

Japanese Kokai Publication Hei-4-15623 discloses a process whichcomprises striking ultrafine black metal oxide particles into thesurface layers of organic polymer particles, while Japanese KokaiPublication Hei-3-101713 discloses a process which comprises dispersingparticles of a polymer containing anionic functional groups in asolution containing an oxidizing agent to let the oxidizing agentadsorbed or impregnated, adding at least one member selected from thegroup consisting of 5-membered heterocyclic compounds and aromatichydrocarbons, and causing the mixture to undergo chemical oxidativepolymerization. Disclosed in Japanese Kokoku Publication Hei-4-27242 isa process in which particles of a water-soluble polymer available uponpolymerization of an ethylenically unsaturated sulfonic acid compound ora salt thereof are dyed with a basic dye.

Furthermore, Japanese Kokai Publication Hei-3-351639 discloses a processwhich comprises dyeing polymer particles comprising amino resin with anacidic dye in the presence of a solvent at high temperature, whileJapanese Kokai Publication Hei-4-363331 discloses a process whichcomprises dispersing an oily solution of an oily dye uniformly in anaqueous medium, mixing the resulting dye emulsion with an emulsion ofpolymer particles so as to dye the particles.

However, this technology of coloring polymer particles preparedbeforehand not only entails high production costs but also has thedrawback that the performance and quality charcteristics of the finalproduct cannot be easily controlled.

The technology which comprises dyeing polymer particles in the course oftheir manufacture includes the following and other processes. JapaneseKokoku Publication Sho-50-33821, Japanese Kokoku PublicationSho-56-50883, and Japanese Kokoku Publication Hei-4-89805 disclosetechnologies for producing liquid crystal display cell spacers in whicha polymerizable monomer is suspension-polymerized in the presence of apigment. However, these methods have limitations in the kind ofpolymerizable monomer that can be used and in production scale and,moreover, the incorporated pigment tends to be exposed on the spacersurface with the result that the pigment itself dissolves out uponexposure to an organic solvent or the like or that impurities in thepigment are liable to dissolve out.

Japanese Kokoku Publication Hei-4-59321 discloses a process forproducing a liquid crystal display cell spacer which comprises mixing alipophilicity-imparted pigment with a monomeric component comprising apolyfunctional vinyl compound and an lipophilic vinyl compound andsubjecting the mixture to suspension-polymerization in an aqueousmedium. This process is conducive to improvements in the dispersibilityof the pigment and solvent resistance but in order to insure asubstantial absence of the pigment on the spacer surface, the vinylcompound must be subjected to a suspension polymerization or emulsionpolymerization as a post-treatment. Since this process involves twostages of polymerization, the production cost is high of necessity.

Japanese Kokai Publication Hei-7-2913 describes a process for producinga liquid crystal display cell spacer which comprises mixing a pigmentuniformly with a (meth) acrylonitrile-containing polyfunctionalethylenically unsaturated component and subjecting the mixture tosuspension polymerization in an aqueous medium. However, this technologycannot provide a liquid crystal display cell spacer colored to a deepshade, for although it is conducive to improvements in thedispersibility of the pigment and the mechanical strength and solventresistance of the spacer, the impurities in the pigment tend to dissolveand diffuse into the spacer to reduce its electrical resistance of thespacer, so that there is a limit to the proportion of the pigment thatcan be added.

Thus, by the technology of coloring polymer particles in the course ofmanufacture thereof, too, it is difficult to obtain a liquid crystaldisplay cell spacer with good coloring effect and light shielding effectand physical properties necessary for a spacer in an expedient andefficient manner.

SUMMARY OF THE INVENTION

The present invention has for its object to solve the above problems andaccordingly provide a liquid crystal display cell spacer with improvedcoloring effect and light shielding effect and satisfactory electrical,physical, chemical, and optical properties and a liquid crystal displaycell with use thereof.

The present invention relates, in a first aspect, to a liquid crystaldisplay cell spacer comprising surface-coated carbon black. This liquidcrystal display cell spacer can be advantageously applied to liquidcrystal display cells.

The present invention relates, in a second aspect, to a liquid crystaldisplay cell spacer comprising a pigment component comprising carbonblack and at least one set of organic pigments of dissimilar colorsother than carbon black. This liquid crystal display cell spacer can beadvantageously applied to liquid crystal display cells.

The present invention relates, in a third aspect, to a liquid crystaldisplay cell spacer comprising a pigment component comprisingsurface-coated carbon black and at least one set of organic pigments ofdissimilar colors other than carbon black. This liquid crystal displaycell spacer can be advantageously applied to liquid crystal displaycell.

The present invention relates, in a fourth aspect, to a liquid crystaldisplay cell comprising the liquid crystal display cell spacer accordingto said first, second, or third aspect of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing one embodiment of the liquid crystaldisplay cell according to the present invention; in which the referencenumeral 1 represents a transparent substrate, 2 a transparent electrode,3 an alignment layer, 4 a transparent substrate, 5 a transparentelectrode, 6 an orientation control film, 7 a substrate, 8 a spacer, 9 asubstrate, 10 a sealing member, 11 nematic liquid crystals, 12 apolarizing sheet, and 13 a polarizing sheet.

DISCLOSURE OF THE INVENTION

The first aspect of the present invention relates to a liquid crystaldisplay cell spacer comprising surface-coated carbon black.

The carbon black for use in this first aspect of the invention has acoated surface which precludes dissolution and diffusion of itsimpurities. By using this surface-coated carbon black, the electricalresistance of the liquid crystal display cell spacer can be preventedfrom reducing even if its proportion is increased and, moreover, thedispersibility of carbon black is improved so that sufficiently deepblack shading of the spacer can be achieved with a smaller amount ofcarbon black. The coating can be applied by, for example, using athermoplastic resin.

As used throughout this specification, the term “impurities” means thecontaminants which are unavoidably contained in ordinary carbon blackand, if dissolved out and diffused into the liquid crystal display cellspacer, reduce the electrical resistance of the spacer, such as sodiumion, potassium ion, chloride ion, and sulfate ion, among others.

The carbon black for said surface-coated carbon black is notparticularly restricted in kind, thus including but not limited tochannel black, roll black, furnace black, and thermal black.

The thermoplastic resin is not particularly restricted in kind butincludes alkyd resin, modified alkyd resin, phenolic resin, naturalresin-modified phenolic resin, maleic acid resin, natural resin-modifiedmaleic acid resin, fumaric acid resin, ester gum, rosin, petroleumresin, coumarone resin, indene resin, polyester resin, polyamide resin,polycarbonate resin, polyethylene resin, epoxy resin, styrene resin,vinyl resin, acrylic resin, chlorinated rubber, benzoguanamine resin,urea resin, etc. These resins may be used independently or incombination.

The technique for coating the surface of carbon black with theabove-mentioned thermoplastic resin is not restricted. A typical methodcomprises pulverizing carbon black in the presence of a hydrophobicmedium containing said thermoplastic resin by means of a crusher such asa ball mill or the like. An alternative method comprises mixing anaqueous dispersion of carbon black with a hydrophobic medium containingsaid thermoplastic resin to prepare an emulsion and removing water byheating. In a further alternative process, a hydrophobic mediumcontaining said thermoplastic resin is heated beforehand,an aqueousdispersion of carbon black is added with stirring, and the water issimultaneously distilled off. The surface-coated carbon black thusobtained can be precipitated by mixing the system with a lower alcohol,e.g. ethanol or isopropyl alcohol, which is miscible with thehydrophobic medium, and recovered by filtration or decantation.

The liquid crystal display cell spacer according to the first aspect ofthe invention can be produced by dispersing said surface-coated carbonblack uniformly in a polymerizable monomer and subjecting the dispersionto polymerization reaction. The method for this polymerization is notparticularly restricted. Thus, for example, suspension polymerizationand emulsion polymerization can be mentioned. Particularly in order toprovide a uniformly colored liquid crystal display cell spacer, asuspension polymerization process is preferred.

The suspension polymerization is carried out by dispersing saidsurface-coated carbon black uniformly in said polymerizable monomer andsubjecting the dispersion to polymerization in the presence of apolymerization initiator in an aqueous medium.

There is no particular limitation on the polymerizable monomer that canbe used, thus including unsaturated carboxylic acids such as acrylicacid, methacrylic acid, maleic acid, maleic anhydride, fumaric acid,crotonic acid, itaconic acid,etc.; acrylic esters such as methylacrylate, ethyl acrylate,n-propyl acrylate, isopropyl acrylate, n-butylacrylate, t-butyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate,etc.; methacrylic esters such as methyl methacrylate, ethylmethacrylate, propyl methacrylate, n-butyl methacrylate, t-butylmethacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, stearylmethacrylate, dodecyl methacrylate, glycidyl methacrylate,β-hydroxyethyl methacrylate, hydroxymethyl methacrylate, etc.; styrenicmonomers such as styrene, vinyltoluene, α-methylstyrene,p-methoxystyrene, t-butylstyrene, chlorostyrene, etc.; diene typemonomers such as butadiene, isoprene, etc.; ethylene, vinyl chloride,vinyl acetate, vinyl propionate, acrylamide, methacrylamide,acrylonitrile, methylolacrylamide, vinyl stearate, acryl acetate,diallyl adipate, dimethyl itaconate, diethyl maleate, allyl alcohol,vinylidene chloride, vinylpyridine, N-vinylpyrrolidone,N-hydroxyacrylamide, 2-vinyl-2-oxazoline, 2-isopropenyl-2-oxazoline,dimethylaminoethyl acrylate, glycidyl methacrylate, allyl glycidylether, monomethyl fumarate, etc. These monomers can be usedindependently or in combination and there is no particular limitation onthe kinds of monomers to be used in combination.

In addition to the polymerizable monomer mentioned above, one or moreother crosslinking compounds can be optionally employed. Among suchoptional monomers can be mentioned aromatic divinyl compounds such asdivinylbenzene, divinylnaphthalene and their derivatives;diethylenically or triethylenically unsaturated carboxylic esters suchas ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, trimethylolpropanetri(meth)acrylate, 1,3-butanediol di(meth) acrylate, etc.; divinylcompounds such as N,N-divinylaniline, divinyl ether, divinyl sulfide,divinyl sulfone, etc.; and compounds each containing 3 or more vinylgroups. The preferred proportion of such crosslinking compounds is 0.005to 100 weight percent based on the combined amount of the crosslinkingcompound and the polymerizable monomer.

The proportion of said polymerizable monomer per 100 parts by weight ofthe aqueous medium is preferably 1 to 200 parts by weight. If theproportion is less than 1 part by weight, the production cannot beprofitably carried out. On the other hand, if the upper limit of 200parts by weight is exceeded, it will be difficult to remove the heat ofpolymerization.

The proportion of surface-coated carbon black is preferably 0.1 to 200parts by weight relative to 100 parts by weight of the polymerizablemonomer. If the proportion is smaller than 0.1 part by weight, thespacer can hardly be colored to a deep shade. On the other hand, if theupper limit of 200 parts by weight is exceeded, the mechanical strengthof the product liquid crystal display cell spacer tends to besacrificed.

In order that the surface-coated carbon black may be uniformly dispersedin said polymerizable monomer, a mechanical device such as a ball mill,bead mill, sand mill, attriter, sand grinder, nanomizer, or the like canbe used with advantage. In this operation, a dispersing agent can beused to improve dispersibility of the surface-coated carbon black.

The dispersing agent that can be used is not particularly restricted inkind. Thus, it may be any of water-soluble polymers such as polyvinylalcohol, starch, methylcellulose, carboxymethylcellulose,hydroxyethylcellulose, poly(sodium methacrylate), etc.; barium sulfate,calcium sulfate, aluminum sulfate, calcium carbonate, calcium phosphate,talc, clay, diatomaceous earth, metal oxide powder, etc.

The proportion of said dispersing agent is 0.01 to 20 weight % based onthe polymerizable monomer component.

The aqueous medium that can be used is not particularly restricted inkind and may for example be an aqueous solution of a water-solubleorganic compound such as polyvinyl alcohol, polyacrylic acid,polymethacrylic acid, gelatin, methylcellulose, polymethacrylamide,polyethylene glycol, polyethylene oxide monostearate, sorbitantetraoleate, glycerin monooleate, dodecylbenzenesulfonic acid, etc., aswell as water.

In the above aqueous medium is in a microfine fashion suspended auniform dispersion of surface-coated carbon black in said polymerizablemonomer. This suspending operation can be carried out using ahomogenizer or the like.

The reaction temperature preferred for said suspension polymerization is20 to 100° C. If the temperature is below 20° C. the polymerizationreaction rate will not be acceptably high. On the other hand, if thereaction temperature exceeds 100° C., the polymerization reaction canhardly be controlled.

The suspension polymerization time is preferably 1 to 50 hours. If thereaction time is less than 1 hour, the rate of polymerization will betoo low. On the other hand, a prolonged reaction over 50 hours isunnecessary.

The liquid crystal display cell spacer obtained by the 5 abovesuspension polymerization reaction can be separated by filtration,centrifugation or other known procedure. The separated liquid crystaldisplay cell spacer is rinsed with water or the like and dried byheating or in vacuo.

The polymerization initiator that can be used in said suspensionpolymerization is not particularly restricted, thus including but notlimited to azo compounds such as 2,2′-azobisisobutyronitrile,2,2′-azobis-2,4′-dimethylvaleronitrile, 2,2′-azobis-methylbutyronitrile,2,2′-azobis-methylheptonitrile, 2,2′-azobis-2,3-dimethylbutyronitrile,2,2′-azobis-2,3,3-trimethylbutyronitrile,2,2′-azobis-2-isopropylbutyronitrile, 4,4-azobis-4-cyanovaleric acid,dimethyl-2,2′-azobisisobutyrate, etc. and organic peroxides such asacetyl peroxide, decanoyl peroxide, lauroyl peroxide, benzoyl peroxide,octanoyl peroxide, orthomethoxybenzoyl peroxide, p-chlorobenzoylperoxide, 2,4-dichlorobenzoyl peroxide, diisopropyl peroxycarbonate,2-ethylhexyl peroxydicarbonate, acetyl cyclohexanesulfonyl peroxide,t-butyl peroxyisobutyrate, t-butyl peroxypivarate, t-butylperoxy-2-ethylhexanoate, di-t-butyl peroxide, t-butyl cumyl peroxide,dicumyl peroxide, methyl ethyl ketone peroxide, cumene hydroperoxide,t-butyl hydroperoxide, etc.

The amount of said polymerization initiator is 0.01 to 30 parts byweight based on 100 parts by weight of the polymerizable monomer. If theproportion is smaller than 0.01 part by weight, the rate ofpolymerization reaction will be too low. On the other hand, addition ofthe initiator in excess of 30 parts by weight is unnecessary. Thepreferred range is 0.1 to 10 parts by weight.

The preferred liquid crystal display cell spacer according to the firstaspect of the present invention has a mean particle diameter of 0.5 to500 μm. If the mean particle diameter is less than 0.5 μm, the particlestend to coagulate and will not be practically useful. The spacer with amean particle diameter exceeding 500 μm will find little application.The preferred range is 1 to 300 μm.

The coefficient of variation of the particle size of the liquid crystaldisplay cell spacer according to the first aspect of the presentinvention is preferably not greater than 20%. If the coefficient ofvariation exceeds 20%, the particle size distribution will be too broadso that the performance of the spacer tends to be sacrificed. Morepreferably, the coefficient of variation is not greater than 10%. Forstill better results, the coefficient is not greater than 5%.

In order to preclude dissolution and diffusion of impurities etc.(inclusive of the pigment itself) and impart an interfacial chemicalmodification to the surface of the liquid crystal display cell spacer,the spacer surface may be coated with a coating material such as asilane coupling agent as necessary. The coating agent is preferablyapplied in a monomolecular layer or as a thin polymer film.

The silane coupling agent that can be used as above is not particularlyrestricted, thus including but not limited to amino silane couplingagents such as γ-aminopropyltrimethoxy silane,N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane,3-[N-allyl-N-(2-aminoethyl)]aminopropyltrimethoxysilane,3-(N-allyl-N-glycidyl)aminopropyltriethoxysilane,3-(N-allyl-N-methacryl)aminopropyltrimethoxysilane, 3-(N,N-diglycidyl)aminopropyltrimethoxysilane, etc.; amide silane coupling agents such asN,N-bis[3-(methyldimethoxysilyl)propyl]amine,N,N-bis[3-(trimethoxysilyl)propyl]amine,N,N-bis[3-(methyldimethoxysilyl)propyl]ethylenediamine,N,N-bis[3-(trimethoxysilyl)propyl]ethylenediamine,N-glycidyl-N,N-bis[3-(methyldimethoxysilyl)propyl]amine,N-glycidyl-N,N-bis[3-(trimethoxysilyl)propyl]amine, etc., vinyl silanecoupling agents such as vinyltriethoxysilane,vinyl-tris(2-methoxyethoxy)silane, etc.; methacrylic silane couplingagents such as γ-methacryloxypropyltrimethoxysilane etc.; glycidylsilane coupling agents such as γ-glycidoxypropyltrimethoxysilane etc.;and mercaptosilane coupling agents such asγ-mercaptopropyltrimethoxysilane etc.

There is no particular limitation on the method for covering the surfaceof the liquid crystal display cell spacer with said coating agent. Atypical method comprises mixing the coating agent with the liquidcrystal display cell spacer in an inorganic solvent such as water or anorganic solvent such as alcohol, heating the mixture with stirring,thereafter separating the liquid crystal display cell spacer by, forexample, decantation, and finally removing the solvent by drying invacuo. An alternative method comprises mixing said coating agent withthe liquid crystal display cell spacer directly and heating the mixture.

The liquid crystal display cell spacer according to the first aspect ofthe present invention comprises a surface-coated carbon black and,therefore, is free from the dissolution and diffusion of any impuritiesin the carbon black, with the result that not only a uniform deep blackshade but also a high solvent resistance can be obtained. Furthermore,the surface-coated carbon black is suppressed in the loss of electricalresistance and improved in dispersibility compared with the uncoatedcarbon black, with the result that it is uniformly dispersed and impartsa higher degree of darkness to the liquid crystal display cell spacer.

The second aspect of the present invention relates to a liquid crystaldisplay cell spacer which comprises a pigment component comprisingcarbon black and at least one set of organic color pigments ofdissimilar colors other than carbon black.

There is no particular limitation on the kind of carbon black that canbe used, thus including but not limited to acetylene black, channelblack, and furnace black. In this second aspect of the invention, asurface-treated carbon black such as Microlith (Ciba-Geigy) can be usedfor improved in carbon black dispersibility.

Referring to said one set of organic color pigments of dissimilar colorsother than carbon black, those organic color pigments which arecomparatively high in transparency and high in heat resistance, weatherresistance, and solvent resistance are preferably used. Particularlypreferred is a set of organic color pigments which, upon admixture, givea substantially black shade. In this second aspect of the invention, atleast one such set of organic color pigments is used.

The color pigments constituting said set of organic color pigments ofdissimilar colors other than carbon black are not restricted in kind butcan for example be selected from among azo and condensed azo organiccolor pigments such as Brilliant Carmine BS, Lake Carmine FB, BrilliantFast Scarlet, Lake Red 4R, Permanent Red R, Fast Red FGR, ToluidineMaroon, Bisazo Yellow, Fast Yellow G, Bisazo Orange, Vulcan Orange,Pyrazolone Red, etc.; organic color pigments in the phthalocyanineseries, such as phthalocyanine Blue, Fast Sky Blue, phthalocyanineGreen, etc.; lake series organic color pigments such as Lake Yellow,Rose Lake, Violet Lake, Blue Lake, Green Lake, etc.; oxazine seriesorganic color pigments; and quinophthalone series organic colorpigments, among others.

Referring to said one set of organic color pigments of dissimilar colorsother than carbon black, two or more of the above-mentioned colorpigments can be selectively employed.

The combination of said organic color pigments constituting said one setof organic color pigments of dissimilar colors other than carbon blackis preferably such that when said at least one set of organic colorpigments of dissimilar colors other than carbon black is used inconjunction with said carbon black, the maximum spectral transmittanceof the liquid crystal display cell spacer according to the second aspectof the present invention over the entire visible wavelength region fromabout 400 to about 700 nm is less than 3% and the total lighttransmittance over the entire visible wavelength region is 0.1 to 2.5%.The more preferred combination is such that the maximum spectraltransmittance value is less than 2.7% and the total light transmittancevalue is 0.2 to 2.0%.

There is no particular limitation on such combination. For example, suchcombinations as blue and violet pigments, red and blue pigments, yellow,blue, and violet pigments, green, blue, and violet pigments, and red,blue, and violet pigments can be mentioned.

From the standpoints of optical transmittance and uniformity of filmsurface, the organic pigments are preferably not greater than 1 μm inparticle diameter.

In the pigment component, the preferred proportion of said carbon blackis 5 to 60 weight % and the preferred proportion of said at least oneset of organic color pigments of dissimilar colors other than saidcarbon black is 95 to 40 weight %. If the proportion of said carbonblack is less than 5 weight % and the proportion of said at least oneset of organic color pigments of dissimilar colors other than saidcarbon black is greater than 95 weight %, the excessive amount of saidat least one set of organic color pigments other than said carbon blacktends to detract from the mechanical strength of the liquid crystaldisplay cell spacer according to the second aspect of the presentinvention.

If the proportion of said carbon black exceeds 60 weight % and that ofsaid at least one set of organic color pigments of dissimilar colorsother than said carbon black is less than 40 weight %, the excessiveamount of carbon black leads to an amplified influence of impuritiesdissolving and diffusing out of the carbon black so that the electricalresistance of the liquid crystal display cell spacer of the secondaspect of the invention tends to be decreased. More preferably, theproportion of said carbon black is 10 to 40 weight % and that of said atleast one set of organic color pigments of dissimilar colors other thancarbon black is 90 to 60 weight %

If the pigment component consists solely of said at least one set oforganic color pigments of dissimilar colors other than said carbonblack, even if the color pigments constitute the optimum combination forrendition of sufficient darkness, the increased amount of said set oforganic color pigments may detract from the mechanical strength of theliquid crystal display cell spacer.

Since the color component of the liquid crystal display cell spacer ofthe second aspect of the invention comprises carbon black and at leastone set of organic color pigments of dissimilar colors other than carbonblack, the necessary amount of carbon black can be smaller so that thedissolution and diffusion of impurities are decreased. Moreover, thedecrease in electrical resistance can be prevented and, at the sametime, sufficient darkness and satisfactory physical properties can besecured.

The liquid crystal display cell spacer according to the second aspect ofthe invention can be obtained by dispersing said pigment componentcomprising said carbon black and said at least one set of organic colorpigments of dissimilar colors other than said carbon black uniformly ina polymerizable monomer and causing the mixture to polymerize. There isno particular limitation on the method of polymerization. Thus,suspension polymerization and emulsion polymerization can be mentionedby way of example but in order to obtain a uniformly colored liquidcrystal display cell spacer, a suspension polymerization process ispreferred.

The suspension polymerization process comprises dispersing said pigmentcomponent uniformly in said polymerizable monomer and causing themixture to polymerize in the presence of a polymerization initiator inaqueous medium.

The polymerizable monomer that can be used includes the same monomers asmentioned for the first aspect of the invention.

One or more suitable crosslinking compounds can be used in combinationwith said polymerizable monomer. The kind of crosslinking compound andits proportion may be similar to those mentioned for the first aspect ofthe invention.

The proportion of said pigment component is preferably 1 to 180 parts byweight based on 100 parts by weight of said polymerizable monomer. Ifthe proportion is less than 1 part by weight, the cell spacer may hardlybe colored to a deep shade, while the mechanical strength of the spacertends to be sacrificed if the pigment component accounts for more than180 parts by weight. The particularly preferred range is 3 to 160 partsby weight.

For dispersing said pigment component uniformly in said polymerizablemonomer, the same machine as mentioned for the first aspect of theinvention, for instance, can be employed.

A dispersing agent may be added for improved dispersibility of saidpigment component. The kind of dispersing agent and its amount may besimilar to those mentioned for the first aspect of the invention.

The aqueous medium may also be the same medium as mentioned for thefirst aspect of the invention.

A uniform dispersion of the pigment component in the polymerizablemonomer is suspended in a microfine fashion in said aqueous medium. Thissuspending operation can be performed using a homogenizer or the like.

The temperature of suspension polymerization may be similar to thatmentioned for the first aspect of the invention.

The polymerization time of suspension polymerization may be similar tothat mentioned for the first aspect of the invention.

The liquid crystal display cell spacer obtained by the above suspensionpolymerization can be isolated by, for example, filtration orcentrifugation. The isolated spacer is rinsed with water or the like anddried by heating or in vacuo.

The polymerization initiator and its amount may for example be similarto those mentioned for the first aspect of the invention.

The mean particle diameter and coefficient of variation of particle sizeof the liquid crystal display cell spacer according to the second aspectof the invention may be similar to those mentioned for the first aspectof the invention.

Where necessary, the liquid crystal display cell spacer according to thesecond aspect of the present invention may have been surface-coated witha coating material such as a silane coupling agent. The silane couplingagent can be selected from among the compounds mentioned for the firstaspect of the invention.

Since the liquid crystal display cell spacer according to the secondaspect of the invention contains a pigment component comprising carbonblack and at least one set of organic color pigments of dissimilarcolors other than carbon black, it not only assumes a deep black colordespite the small proportion of the pigment component but also hassatisfactory electrical resistance. Moreover, chances for contaminationof the liquid crystals due to the pigment component are minimized.

The third aspect of the present invention is a liquid crystal displaycell spacer comprising a pigment component comprising surface-coatedcarbon black and at least one set of organic color pigments ofdissimilar colors other than carbon black.

The carbon black for use in this third aspect of the invention has beensurface-coated for preventing the dissolution and diffusion ofimpurities. The surface-coated carbon black may be selected from amongthose species of carbon black mentioned for the first aspect of theinvention.

The above-mentioned set of organic color pigments of dissimilar colorsother than carbon black and its proportion can be similar to thosementioned for the second aspect of the invention.

The liquid crystal display cell spacer according to the third aspect ofthe invention can be produced by using said surface-coated carbon blackin otherwise the same manner as described for the liquid crystal displaycell spacer according to the second aspect of the invention.

The mean particle diameter and coefficient of variation of particle sizeof the liquid crystal display cell spacer according to the third aspectof the invention are similar to those mentioned for the first aspect ofthe invention.

Where necessary, the liquid crystal display cell spacer according to thethird aspect of the invention may have been covered with a coatingmaterial such as a silane coupling agent. The silane coupling agent maybe selected from among the compounds mentioned for the first aspect ofthe invention.

Since the liquid crystal display cell spacer according to the thirdaspect of the invention contains a surface-coated carbon black, there islittle dissolution and diffusion of impurities into the spacer. Thiseffect coupled with the effect of concomitant use of at least one set oforganic color pigments of dissimilar colors other than carbon blackresults in a black shade even if the smaller amount of carbon black isused as compared with the first and the second aspect of the inventionand insures high solvent resistance, electrical resistance andmechanical strength.

The fourth aspect of the present invention is a liquid crystal displaycell incorporating said liquid crystal display cell spacer according tothe first, second, or third aspect of the present invention.

The liquid crystal display cell according to the fourth aspect of theinvention gives an excellent display image contrast without the spacerbeing visually recognized as luminescent spots in the dark or black areaof the image.

An embodiment of the liquid crystal display cell according to the fourthaspect of the invention is. now described with reference to theaccompanying drawings.

As shown in FIG. 1, a liquid crystal display cell A comprises a pair ofsubstrates 7, 9, a spacer 8, a sealing member 10, a nematic liquidcrystalline component 11, and polarizing sheets 12, 13.

The spacer 8 is disposed between the substrates 7 and 9 constitutingsaid pair for the purpose of maintaining a predetermined gap between thesubstrates 7 and 9. The sealing member 10 is disposed around said pairof substrates 7, 9. The nematic liquid crystal line component 11 issealed in the space between said substrates 7 and 9. The polarizingsheets 12 and 13 are bonded to the surfaces of the substrates 7 and 9,respectively.

Each of the substrates 7 and 9 comprises a transparent glass substrate 1or 4 with a transparent electrode 2 or 5 formed upon a pattern on oneside thereof and an alignment layer 3 or 6 (e.g. a polyimide film)coated on the surface of the transparent electrode (2 or 5)-transparentsubstrate (1 or 4) assembly. The alignment layer 3 or 6 has been treatedto control alignment by rubbing.

The spacer 8 is a liquid crystal display cell spacer according to thefirst, second, or third aspect of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The following examples are intended to illustrate the present inventionin further detail and should by no means be construed as defining thescope of the invention.

EXAMPLE 1

Preparation of a Liquid Crystal Cell Spacer

To a uniform mixture of 60 parts by weight of tetramethylolmethanetriacrylate, 20 parts by weight of divinylbenzene, and 20 parts byweight of acrylonitrile was added 12 parts by weight ofpolyethylene-coated carbon black and the carbon black was uniformlydispersed by means of a bead mill for 48 hours.

This colored polymerizable monomer mixture in which said surface-coatedcarbon black had been dispersed was evenly mixed with 2 parts by weightof benzoyl peroxide and the mixture was poured in 850 parts by weight ofa 3 weight % aqueous solution of polyvinyl alcohol. After thoroughstirring, the mixture was suspended with a homogenizer so that thediameter of droplets of the colored polymerizable monomer would be about3 to 10 μm to provide a suspension.

This suspension was transferred to a 2-L separable flask equipped with athermometer, stirrer, and reflux condenser and heated at 85° C. in anitrogen gas atmosphere with constant stirring. This polymerizationreaction was carried out for 7 hours, at the end of which time thetemperature was increased to 90° C. and the reaction mixture wasmaintained at that temperature for 3 hours to carry the polymerizationreaction to completion. This polymerization reaction mixture was cooledand the resulting colored particles were recovered by filtration, rinsedwell with water, and dried to provide 120 parts by weight of coloredparticles containing dispersing pigment within the size range of 3 to 10μm. These colored particles were subjected to classification to providea liquid crystal display cell spacer with a mean particle diameter of5.55 μm and a coefficient of variation in particle size of 2.48%.

The degree of darkness (light transmittance) of the liquid crystaldisplay cell spacer thus obtained, the concentration of impurities inthe spacer, and the electrical resistance of the spacer were evaluatedby the following methods. The results are presented in Table 1.

Evaluation Methods

(1) Degree of darkness

A mixture of the polymerizable monomer of the same composition as thatof the above liquid crystal display cell spacer and the color componentwas polymerized to prepare a 1 mm-thick wafer. The spectraltransmittance of this wafer was measured over the entire visiblewavelength range of 400 to 700 nm with a spectrophotometer and themaximum value was regarded as the degree of darkness of the liquidcrystal display cell spacer.

(2) The concentrations of impurities in the liquid crystal display cellspacer

Ten (10) grams of the liquid crystal display cell spacer obtained wasput in 330 ml of a solvent mixture (water/isopropyl alcohol =7/3, v/v)with stirring and the mixture was allowed to stand at room temperaturefor one week (with stirring once a day). The mixture was allowed tostand without agitation in the final 2-day period to let the liquidcrystal display cell spacer settle. The supernatant was recovered with afilter paper (0.2 μm thick), concentrated to 30 ml, and analyzed. Theanalyses for sodium and potassium ions were carried out with Jarrell-AshSPQ8000 atomic absorption spectrophotometer. The analyses for chlorideand sulfate ions were carried out with Dionex 2010I ion chromatographicanalyzer.

(3) Electrical resistance of the liquid crystal display cell spacer

Using Toa Dempa Ultra Megohmmeter SM-8210, the liquid crystal displaycell spacer was filled into the accessory liquid sample electrode andthe electrical resistance of the liquid crystal display cell spacer wasmeasured according to the instruction manual for liquid samples.

Fabrication of a TN Liquid Crystal Display Cell

In order to evaluate the performance of a liquid crystal display deviceincorporating the liquid crystal display cell spacer obtained, a TNliquid crystal display cell of the normally black display mode, whichfaciliates assessment of the light shielding effect of spacers, wasfabricated. The light shielding effect of the spacer or the effect oncell gap formation as evaluated using this test liquid crystal displaycell is translatable to the effect obtainable with an STN or otherliquid crystal display cell, so that the results of evaluation are notexclusively valid for TN liquid crystal display cells but valid for allkinds of liquid crystal display cells.

A transparent electrically conductive indium oxide-tin oxide film wasformed in a thickness of about 500 Angstrom units on a 0.7 mm-thickglass sheet by the low-temperature sputtering technique and apredetermined electrode pattern was formed by photolithography. Then,the surface was coated with an alignment material and heated to obtainan alignment layer. This glass sheet was cut to 5 cm×12.5 cm to provideglass substrates for a liquid crystal display cell.

The peripheral edge of the glass substrate obtained was then printedwith a glass fiber spacer-mixed epoxy adhesive in a breadth of 1 mm bythe screen printing technique.

After this glass substrate was set in a horizontal position, the liquidcrystal display cell spacer was scattered over with the aid ofpressurized nitrogen gas and allowed to fall uniformly on the glasssubstrate. The scattering time was adjusted so that the density of theliquid crystal display cell spacer particles on the glass substratewould be about 150 particles/mm².

After another glass substrate was superimposed on the liquid crystaldisplay cell spacer-scattered glass substrate, a load of 1 kg/cm² wasapplied uniformly on the whole glass substrate by means of a press. Atthe same time, the assembly was heated at a temperature of 160° C. for20 minutes to cure the peripheral epoxy adhesive.

After a vacuum was established in the fabricated cell by aspiration, theliquid crystal was injected from a bore formed in a part of theperipheral seal and the injection bore was closed up under asubatmospheric intracellular pressure of 0.6 atmosphere. The cell wasthen heated to a predetermined temperature for liquid crystalrealignment to provide a finished liquid crystal display cell.

The measured gap between the top and bottom substrates of this liquidcrystal display cell was 5.38 μm.

Evaluation Methods

(1) Unevenness of color of the TN liquid crystal display cell

Polarizing sheets were set on either surface of the liquid crystaldisplay cell so that the color of the reflecting light of the lightprojected against the TN liquid crystal display cell would be olive. Theolive color was uniform all over without unevenness.

The following evaluation criteria were used.

⊚: no color unevenness

◯: a practically acceptable degree of color unevenness

X: a practically unacceptable degree of color unevenness

(2) The light shielding effect of the cell spacer in the TN

Liquid Crystal Display Cell

The polarizing sheets bonded to the liquid crystal display cell were setto the TN normally black mode and the assembly was observed under atransmission microscope at ×200 magnification.

With the drive voltage OFF, the darkness in the center of the spacer andthe darkness of the spacer-free liquid crystal area were comparedvisually by using a panel of 10 assessors.

The evaluation was ⊚ when the number of assessors who judged that thedarkness in the center of the spacer was deeper or equivalent accountedfor 80% or more of the panel, ◯ when it accounted for 70 to 80%, A whenit accounted for 50 to 70%, and x when it accounted for less than 50%.

The mean cell gap values and the results of evaluation of colorunevenness and light shielding effect are shown in Table 1.

EXAMPLES 2 to 4

Except that the compositions shown in Table 1 were used, liquid crystaldisplay cell spacers and cells were fabricated and evaluated in the samemanner as in Example 1. The results are shown in Table 1.

COMPARATIVE EXAMPLE 1

Except that uncoated carbon black was used and the composition shown inTable 1 was used, a liquid crystal display cell spacer and a liquidcrystal display cell were fabricated and evaluated in the same manner asin Example 1. The results are shown in Table 1.

COMPARATIVE EXAMPLE 2

Except that the composition shown in Table 1 was used with omission ofcarbon black, a liquid crystal display cell spacer and a liquid crystaldisplay cell were fabricated and evaluated as in Example 1. The resultsare shown in Table 1.

TABLE 1 Comparative Examples Examples 1 2 3 4 1 2 Composi- Polyme-Tetramethylolmethane triacrylate 60 60 60 — 60 60 tion rizableDivinylbenzene 20 20 20 50 20 20 (weight monomer Acrylonitrile 20 20 20— 20 20 part) Ethylene glycol dimethacrylate — — — 50 — — CarbonSurface-coated carbon black 12 6 18 12 — — Carbon black — — — — 30 —Quality Spacer Mean particle size (μm) 5.55 3.59 7.12 4.55 6.05 5.78 andquality Coefficient of variation 2.48 2.66 2.85 2.89 3.71 4.11 perfor-of particle size (%) mance Degree of darkness (spectral 2.6 3.0 2.2 2.51.5 75.7 parame- transmittance) (%) ters Electrical resistance (Ω · cm)10¹⁴ 10¹⁴ 10¹³ 10¹⁴ <10⁹ 10¹¹ Levels Sodium ion (ppm) 0.02 0.01 0.030.02 0.1 0.03 of Potassium ion (ppm) 0.04 0.03 0.05 0.03 0.1 0.05impuri- Chloride ion (ppm) 0.1 0.1 0.2 0.1 0.9 0.3 ties Sulfate ion(ppm) 0.5 0.4 0.7 0.6 1.5 0.5 Cell Mean cell gap (μm) 5.38 3.38 7.034.00 5.63 5.65 quality Evenness of color ⊚ ⊚ ⊚ ⊚ X ⊚ Light shielingeffect ⊚ ◯ ⊚ ⊚ X X

EXAMPLE 5

Preparation of a Liquid Crystal Display Cell Spacer

To a uniform mixture of 60 parts by weight of tetramethylolmethanetriacrylate, 20 parts by weight of divinylbenzene, and 20 parts byweight of acrylonitrile was added 12 parts by weight of carbon black, 6parts by weight of Phthalocyanine Blue (blue pigment), and 6 parts byweight of Dioxane Violet (violet pigment) as the black pigment componentand the black pigment component was evenly dispersed by means of a beadmill for 48 hours.

This colored polymerizable monomer mixture in which said black pigmentcomponent had been dispersed was evenly mixed with 2 parts by weight ofbenzoyl peroxide and the mixture was poured in 850 parts by weight of a3 weight % aqueous solution of polyvinyl alcohol. After thoroughstirring, the mixture was suspended with a homogenizer so that thediameter of droplets of the colored monomer would be about 3 to 10 μm toprovide a suspension.

This suspension was transferred to a 2-L separable flask equipped with athermometer, stirrer, and reflux condenser and heated to 85° C. in anitrogen gas atmosphere with constant stirring. This polymerizationreaction was carried out for 7 hours, at the end of which time thetemperature was raised to 90° C. and the reaction mixture was maintainedat that temperature for 3 hours to carry the polymerization reaction tocompletion. This polymerization reaction mixture was cooled and theresulting colored particles were recovered by filtration, rinsed wellwith water, and dried to provide 120 parts by weight of coloredparticles containing dispersing pigment within the size range of 3 to 10μm. Colored particles obtained were subjected to classification toprovide a liquid crystal display cell spacer with a mean particlediameter of 6.45 μm and a coefficient of variation in particle size of2.88%.

The liquid crystal display cell spacer thus obtained was evaluated inthe same manner as in Example 1, and a liquid crystal display cell wasfabricated and evaluated in the same manner as in Example 1. The resultsare presented in Table 2.

EXAMPLES 6 TO 8 AND COMPARATIVE EXAMPLES 3 AND 4

Except that the compositions shown in Table 2 were used, liquid crystaldisplay cell spacers and cells were fabricated and evaluated in the samemanner as in Example 5. The results are shown in Table 2.

TABLE 2 Comparative Examples Examples 5 6 7 8 3 4 Composi- Polyme-Tetramethylolmethane triacrylate 60 60 60 — 60 60 tion rizableDivinylbenzene 20 20 20 50 20 20 (weight monomer Acrylonitrile 20 20 20— 20 20 part) Ethylene glycol dimethacrylate — — — 50 — — CarbonSurface-coated carbon black — — — — — — Carbon black 12 10 20 25 30 —Pigment Phthalocyanine blue 6 10 5 10 — 15 Dioxazine violet 6 10 5 10 —5 Isoindoline yellow — 10 — — — — Quinacridone red — — 15 — — 20 QualitySpacer Mean particle size (μm) 6.45 4.17 8.63 6.29 7.03 6.72 and qualityCoefficient of variation 2.88 3.10 2.75 2.58 3.54 4.05 perfor- ofparticle size (%) mance Degree of darkness (spectral 2.5 2.8 2.0 1.7 1.676.4 parame- transmittance) (%) ters Electrical resistance (Ω · cm) 10¹⁴10¹⁴ 10¹⁴ 10¹⁹ <10¹¹ 10¹³ Levels Sodium ion (ppm) 0.02 0.02 0.03 0.020.1 0.03 of Potassium ion (ppm) 0.05 0.02 0.03 0.02 0.1 0.03 impuri-Chloride ion (ppm) 0.1 0.2 0.2 0.2 0.8 0.3 ties Sulfate ion (ppm) 0.50.3 0.3 0.4 1.2 0.4 Cell Mean cell gap (μm) 6.04 3.61 8.22 4.87 6.816.32 quality Evenness of color ⊚ ⊚ ◯ ◯ X X Light shielding effect ⊚ ⊚ ⊚◯ Δ X

EXAMPLES 9 and 10

Except that the surface-coated carbon black of Example 1 and thecompositions shown in Table 3 were used, liquid crystal display cellspacers and cells were fabricated and evaluated in the same manner as inExample 5.

The results are shown in Table 3.

TABLE 3 Examples 9 10 Composi- Polyme- Tetramethylolmethane triacrylate50 50 tion rizable Divinylbenzene 30 30 (weight monomer Acrylonitrile 1010 part) Carbon Surface-coated carbon black 6 10 Carbon black — —Pigment Phthalocyanine blue 7 15 Dioxazine violet 7 5 Isoindoline yellow7 5 Quinacridone red 7 20 Quality Spacer Mean particle size (μm) 6.8 4.9and quality Coefficient of variation 2.94 3.6 perfor- of particle size(%) mance Degree of darkness (spectral 2.9 2.7 parame- transmittance)(%) ters Electrical resistance (Ω · cm) 10¹⁴ 10¹⁴ Levels Sodium ion(ppm) 0.02 0.03 of Potassium ion (ppm) 0.02 0.01 impuri- Chloride ion(ppm) 0.2 0.2 ties Sulfate ion (ppm) 0.4 0.5 Cell Mean cell gap (μm)6.49 4.66 quality Evenness of color ⊚ ◯ Light shielding effect ◯ ⊚

INDUSTRIAL APPLICABILITY

Its construction having been described hereinabove, the liquid crystaldisplay cell spacer of the present invention is very satisfactory incoloring effect and light shielding effect and has optimal electrical,physical, chemical, and optical properties. The liquid crystal displaycell in corporating this cell spacer shows a good display contrast ofthe image with the spacer not visualized as luminessent points in thedark area of the image.

What is claimed is:
 1. A liquid crystal display cell spacer comprising apigment component comprising carbon black and at least one set oforganic pigments of dissimilar colors other than carbon black, andhaving a maximum spectral transmittance over the visible wavelengthregion from about 400 to about 700 nm of less than 3% and having a totallight transmittance over the visible wavelength region of 0.1 to 2.5%.2. The liquid crystal display cell spacer of claim 1 wherein the carbonblack is a surface-treated carbon exhibiting improved dispersibility. 3.The liquid crystal display cell spacer of claim 1 wherein the organicpigments are high in transparency, heat resistance, weather resistanceand solvent resistance.
 4. The liquid crystal display cell spacer ofclaim 1 having a maximum spectral transmittance over the visiblewavelength region from about 400 to about 700 nm of less than 2.7% andhaving a total light transmittance over the visible wavelength region of0.2 to 2.0%.
 5. The liquid crystal display cell spacer of claim 1wherein the organic pigments have maximum particle diameter of 1 m. 6.The liquid crystal display cell spacer of claim 1 wherein thepreparation of carbon black is 5 to 60% by weight and that of theorganic pigments is 95 to 40% by weight.
 7. The liquid crystal displaycell spacer of claim 1 which further comprises a polymer.